This invention relates to a retainer which cooperates with a hub on a movable wall to allow a control valve to move between four distinct positions in the operation of a servomotor.
In known servomotors such as illustrated in U.S. Pat. Nos. 3,289,547 and 3,452,646, the operational control valve has three distinct operational positions, i.e., full release, lap and applied. In response to an operator input, the control valve moves from the full release to lap and into the applied position to allow a pressure differential to be created and move a wall to develop a corresponding output force. When the resistance to movement of an output member by the output force is in balance with the input force, the control valve returns to the lap position. On termination of the input force, a return spring and the reaction force move the control valve to the full release position to allow the pressure differential to dissipate. The limit to which the return spring and reaction force can move the control valve is controlled by a retainer such as the key shown in U.S. Pat. No. 3,125,003 and the step on the housing shown in U.S. Pat. No. 3,289,547. On termination of the input force it is important that the control valve move to the fully released position as soon as possible to allow the operational pressure differential to dissipate and thereby terminate the brake application. Unfortunately, in order to effect a brake application, the control valve must move from the fully released position through the lap position to the actuation position. This movement causes a delay in the response time from which an operator decides to make as brake application and an actual brake application occurs. A reduction in response time can reduce the overall stopping distance which could result in preventing damage to property as well as loss of lives.